Photosynthesis

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Outline

• Reproductive Strategies
• Alternation of generations
• Adaptation to a land environment
• Flowers
• Pollination
• Fertilization
• Seed Development
• Fruit
• Seed Germination
• Asexual Reproduction
• Tissue Culture

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Reproductive Strategies

• All plants have a two-stage, alternating life
  cycle
• Sporophyte produces haploid spores by meiosis
• Spores divide mitotically to become haploid
  gametophytes
• Gametophytes produce gametes
• Gametes fuse to produce zygote
• Zygote divides mitotically to become diploid
  sporophyte

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Alternation of Generationsin Flowering Plants
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Reproductive Strategies

• Flower produces two types of spores
• Microspore - Male gametophyte
• Undergoes mitosis
• Becomes pollen grain
• Megaspore - Female gametophyte
• Undergoes mitosis
• Becomes embryo sac within an ovary, within an
  ovule
• Ovule becomes seed

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Flowers

• Flower develops in response to environmental
  signals such as day length
• In monocots, flower parts occur in threes and
  multiples of three
• In eudicots, flower parts occur in fours or fives
  and multiples of four or five

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Anatomy of a Flower
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Monocot vs. Eudicot Flowers
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Flowers

• Leaf-like sepals protect the bud
• Open flower has whorl of petals
• Four whorls of modified leaves attached to a
  receptacle at the end of a flower stalk
• Receptacle with a single flower is a peduncle
• Receptacle with several flowers is a pedicle

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Flowers

• Leaf-like sepals protect the bud
• Open flower has whorl of petals
• Four whorls of modified leaves attached to a
  receptacle at the end of a flower stalk
• Receptacle with a single flower is a peduncle
• Receptacle with several flowers is a pedicle

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Flowers

• Stamens are male portion of flower
• Anther - Saclike container
• Filament - Slender stalk
• Carpel is female portion of flower
• Stigma - Enlarged sticky knob
• Style - Slender stalk
• Ovary - Enlarged base enclosing ovules

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Flowers

• Complete vs. incomplete flowers
• Complete flowers have sepals, petals, stamens,
  and a carpel
• Incomplete flowers missing one or more of above
• Bisexual vs. unisexual flowers
• Bisexual flowers have both stamens and carpel
• Unisexual flowers have one but not the other
• Monoecious vs. dioecious plants
• Monoecious plants have staminate flowers and
  carpellate flowers on the same plant
• Dioecious plants have all staminate or all
  carpellate flowers

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Corn Plants are Monoecious
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Life Cycle of Flowering Plants
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From Spores to Fertilization

• Male Gametophytes
• Microspores are produced in anthers
• Each anther has four pollen sacs, each with many
  microsporocytes
• Undergoes meiosis to produce microspores
• Mitosis produces pollen grains

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Pollination

• Pollination is the transfer of pollen from an
  anther to the stigma of a carpel
• Self-pollination occurs if the pollen is from the
  same plant
• Cross-pollination occurs if the pollen is from a
  different plant

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Pollination
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Production of Female Gametophyte

• Ovary contains one or more ovules
• Ovule has mass of parenchyma cells
• One cell enlarges to become megasporocyte
• Undergoes meiois and becomes four haploid
  megaspores
• Functional megaspore divides mitotically until
  there are eight nuclei of a female gametophyte

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Fertilization

• When pollen grain lands on stigma, it germinates
  forming a pollen tube
• Passes between the stigma and style to reach the
  micropyle of the ovule
• Double fertilization occurs
• One sperm nucleus unites with the egg nucleus,
  producing a zygote
• Other sperm nucleus unites with the polar nuclei,
  forming a 3n endosperm cell

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Seed Development

• Development of eudicot embryo
• After double fertilization, endosperm nucleus
  begins to divide asymmetrically
• Small cell is destined to become the embryo
• Larger cell divides repeatedly to become a
  suspensor

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Development of a Eudicot Embryo
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Monocot vs. Eudicot
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Development of Eudicot Embryo

• During globular stage, prembryo is ball of cells
• Outermost cells will become dermal tissue
• Embryo is heart shaped when cotyledons appear
• Epicotyl is portion between cotyledons
  contributing to shoot development
• Hypocotyl is portion below that contributes to
  stem development
• Radicle contributes to root development

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Fruit Types and Seed Dispersal

• Simple Fruits
• Simple fruits are derived from single or several
  united carpels
• Legumes are fruits that split along two sides
  when mature
• Dehiscent - Split open
• Indehiscent - Fail to split open

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Pea Flower and Pea Pod
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Simple Fruits

• Fleshy
• Drupe
• Berry
• Pome

• Dry
• Follicle
• Legume
• Capsule
• Achene
• Nut
• Grain

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Simple Fruits

• Dispersal
• Many seeds are dispersed by wind
• Woolly hairs, plumes, wings
• Fleshy fruits - Attract animals and provide them
  with food
• Peaches, cherries, tomatoes
• Accessory fruit - Bulk of fruit is not from
  ovary, but from receptacle
• Apples

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Structure and Function of Fruits
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Compound Fruits

• Compound fruits develop from several individual
  ovaries
• Aggregate Fruits
• Ovaries are from a single flower
• Blackberry
• Multiple Fruits
• Ovaries are from separate flowers clustered
  together

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Seed Germination

• When seed germination occurs, the embryo resumes
  growth and metabolic activity
• Length of time seeds retain their viability is
  quite variable
• Some seeds do not germinate until they have been
  through a dormant period
• Temperate zones - Cold Weather
• Deserts - Rain

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Seed Germination

• Environmental requirements for seed germination
• Availability of oxygen for metabolic needs
• Adequate temperature for enzyme activity
• Adequate moisture for hydration of cells
• Light (in some cases)
• Respiration and metabolism continue throughout
  dormancy, but at a reduced level

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Seed Structure and Germinationin the Common
Garden Bean
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Corn Kernel Structure and Germination
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Asexual Reproduction in Plants

• Plants contain nondifferentiated meristem tissue
• Allows them to reproduce asexually by vegetative
  propagation
• Plant hormone auxin
• Can be used to cause roots to develop
• Expands the list of plants that can be propagated
  from cuttings

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Asexual Reproduction in Plants
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Tissue Culture of Plants

• Tissue culture is the growth of a tissue in an
  artificial liquid or solid culture medium
• Plant cells are totipotent
• Meristem culture
• Auxins and cytokinins allow many new shoots to
  develop from a single shoot tip
• Virus-free clonal plants
• Suspension Culture
• Rapidly growing calluses are cut into small
  pieces and shaken into a liquid nutrient medium
• Single cells or small clumps break off and form a
  suspension

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Tissue Culture in Plants
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Genetic Engineering

• Traditionally, hybridization was used to produce
  plants with desirable traits
• Crossing different varieties of plants
• Transgenic plants can now be produced by placing
  foreign genes into a plant
• Agricultural plants with improved traits
• Pest or insecticide resistant
• Commercial Products
• Human hormones, antibodies

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Maize
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Genetically Engineered Plants
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Review

• Reproductive Strategies
• Alternation of generations
• Adaptation to a land environment
• Flowers
• Pollination
• Fertilization
• Seed Development
• Fruit
• Seed Germination
• Asexual Reproduction
• Tissue Culture

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